There has been known an oil separator that separates mist oil contained in target gas from the gas. For example, an oil separator described in Patent Literature 1 includes a cylindrical stationary housing, a cylindrical stationary casing with a ceiling, and a conical partition with an opening on the top surface. These components define a lower chamber and an upper chamber. The lower chamber includes a centrifugal rotor to clean oil. The upper chamber includes a gas cleaning device to clean gas. A lower end of the stationary housing is coupled to a base. The lower chamber is communicated with an internal space of the tubular base.
This tubular base is communicated with a combustion engine. Oil after being cleaned is returned to the combustion engine and gas from a crankcase is introduced to the combustion engine. In the internal space of the tubular base, a tubular fixing member is disposed which fixes the lower end of the shaft. Through the fixing member, oil to be cleaned is supplied.
The centrifugal rotor and the gas cleaning device are coupled with a tubular supporting member and are rotatable around a stationary shaft inserted through the supporting member. The centrifugal rotor internally includes a separation chamber. The oil is supplied to this separation chamber through a clearance between the supporting member and the stationary shaft and through an opening open at the supporting member. After the cleaning in the separation chamber, the supplied oil is discharged to a side portion through discharge ports disposed at a bottom surface of the centrifugal rotor. Discharging the oil generates a driving power to rotate the centrifugal rotor and the gas cleaning device.